The present invention relates essentially to a spark ignited internal combustion engine operated with charge stratification having a main combustion chamber and an auxiliary combustion chamber or prechamber connected to the main combustion chamber by means of a short passage. The auxiliary combustion chamber is provided with a fuel delivery device and an ignition device for igniting a combustible fuel-air mixture which is richer, in fuel content, than the fuel-air-mixture in the main combustion chamber.
Spark ignited internal combustion engines of the type operated with stratified charges have been known for many years. Although many variations of this type of internal combustion engine have been developed, the fundamental concept of all stratified charge engines has been, through structural measures, to diversify the mixture composition of the cylinder charge, at the instant of ignition, in such a manner that an ignitable fuel-rich mixture is present in the immediate vicinity of the spark plug, while the charge in the remaining combustion chamber is adjusted to properly coincide with the prevailing operating conditions of the engine. This latter combustion charge may therefore consist of a fuel-lean mixture or even of air.
Heretofore such engine designs have been aimed at ensuring the safe ignition of the cylinder charge, notwithstanding wide variations in the total mixture composition, and facilitating carburetor-fueled operation at higher compression ratios without reaching the knock limit. Currently, however, the stratified charge method is viewed primarily as an expedient for reducing the noxious substances, e.g., nitric oxides, contained in the engine emissions.
In addition to the internal combustion engines wherein the stratification of the charge is achieved by a precisely timed injection of the fuel into a turbulent stream of air produced in the combustion chamber, other stratified charge internal combustion engines are known wherein the combustion chamber is divided into a main combustion chamber, delimited by the piston, and an auxiliary combustion chamber or prechamber in communication with the main combustion chamber and arranged separately in the cylinder head. The auxiliary combustion chamber is provided with an ignition device, e.g., a spark plug, and a fuel delivery device consisting either of a fuel injection nozzle or an auxiliary intake valve for delivery of a fuel-rich mixture prepared by an auxiliary carburetor. The auxiliary combustion chamber is connected with the main combustion chamber by a short passage so that, following ignition of the fuel-rich charge present in the auxiliary combustion chamber, a flame front can advance into the main combustion chamber for the purpose of igniting the residual cylinder charge in the main combustion chamber. Accordingly, the residual cylinder charge may be much leaner, in fuel content, than the charge in the auxiliary combustion chamber and may be varied in dependence upon the engine load, whereby delayed combustion occurs with lower combustion peak temperatures and peak pressures.
In operation of the internal combustion engines of this type, it has been found that the wall temperature of the auxiliary combustion chamber has a decisive influence on the preparation and homogenization of the fuel-rich mixture in the auxiliary combustion chamber. More particularly, during the cold starting and the warming-up phase of the internal combustion engine, i.e., when the walls of the auxiliary combustion chamber have not yet attained operating temperatures, the fuel of the comparatively fuel-rich mixture present in the auxiliary combustion chamber has a tendency to condense heavily on the cold auxiliary combustion chamber walls. Due to the reduction in the fuel content of the auxiliary combustion chamber mixture caused by this condensation, defective operation of the internal combustion engine occurs resulting in misfiring, stalling, and the like. In an effort to compensate for the reduction in fuel content, an increase in the quantity of fuel delivered to the auxiliary combustion chamber, during these critical operating periods, results in the faulty combustion of the increased quantity of fuel which can be only imperfectly combusted, thereby increasing the noxious substances in the engine emissions.
On the other hand, when the walls of the auxiliary combustion chamber attain excessively high temperatures, resulting from higher loads on the internal combustion engine, there exists the danger of spontaneous ignition. To avert these shortcomings, a temperature ranging from 200.degree. to 300.degree. C. may be considered a favorable wall temperature for the auxiliary combustion chamber. However, it is also desirable that such a temperature range be attained as rapidly as possible after the cold starting of the internal combustion engine and that the temperature be maintained, if possible, throughout the entire operation of the engine.
An internal combustion engine described in German Offenlegungsschrift No. 2,302,015 comprises an auxiliary combustion chamber consisting of a metal tube which is heated by means of an electric heating coil wrapped around the metal tube. However, this design necessitates increased construction cost, due to the structural modifications required to accommodate the heating coil. On the other hand, because the energy consumed by the electric heating coil, in order to effectively heat the auxiliary combustion chamber, creates a considerable additional energy requirement, operating cost is also increased.